Abstract
The observation-based source terms available in the third-generation wave model WAVEWATCH III (i.e., the ST6 package for parameterizations of wind input, wave breaking, and swell dissipation ...terms) are recalibrated and verified against a series of academic and realistic simulations, including the fetch/duration-limited test, a Lake Michigan hindcast, and a 1-yr global hindcast. The updated ST6 not only performs well in predicting commonly used bulk wave parameters (e.g., significant wave height and wave period) but also yields a clearly improved estimation of high-frequency energy level (in terms of saturation spectrum and mean square slope). In the duration-limited test, we investigate the modeled wave spectrum in a detailed way by introducing spectral metrics for the tail and the peak of the omnidirectional wave spectrum and for the directionality of the two-dimensional frequency–direction spectrum. The omnidirectional frequency spectrum
E
(
f
) from the recalibrated ST6 shows a clear transition behavior from a power law of approximately
f
−4
to a power law of about
f
−5
, comparable to previous field studies. Different solvers for nonlinear wave interactions are applied with ST6, including the Discrete Interaction Approximation (DIA), the more expensive Generalized Multiple DIA (GMD), and the very expensive exact solutions using the Webb–Resio–Tracy method (WRT). The GMD-simulated
E
(
f
) is in excellent agreement with that from WRT. Nonetheless, we find the peak of
E
(
f
) modeled by the GMD and WRT appears too narrow. It is also shown that in the 1-yr global hindcast, the DIA-based model overestimates the low-frequency wave energy (wave period
T
> 16 s) by 90%. Such model errors are reduced significantly by the GMD to ~20%.
An analytical treatment of an earth and rockfill dam in a radially inhomogeneous multi-layered semi-cylindrical canyon in a half-space under obliquely incident plane SH waves is presented. In terms ...of a radial wave function expansion and a transfer matrix approach, a rigorous approach is formulated to consider inhomogeneity of the deformable canyon and associated phenomena of wave redirection, reflection, transmission, scattering and concentration. Upon confirmation of its accuracy with a past exact solution for the degenerated case of a dam in a homogeneous canyon, the multi-layer solution is extended to the case of a dam in a canyon covered by a surficial zone with a power-law shear-wave velocity model as a generalized class of smooth in-situ variations. A comprehensive set of numerical examples are presented to illustrate the sensitivity of the dam response to the inhomogeneity profile of the top canyon zone, the frequency content and the angle of the seismic wave incidence. As illustrated in both frequency and time domains, wave concentration is found to be the main reason for the high amplifications of the displacement within the dam.
•Analytical solution to a dam-inhomogeneous canyon system under SH waves is proposed.•Both canyon's topography and its depth-wise material variation affect dam response.•Key features of wave scattering and concentration phenomena are demonstrated.
R/V Lance serendipitously encountered an energetic wave event around 77°N, 26°E on 2 May 2010. Onboard GPS records, interpreted as the surface wave signal, show the largest waves recorded in the ...Arctic region with ice cover. Comparing the measurements with a spectral wave model indicated three phases of interaction: (1) wave blocking by ice, (2) strong attenuation of wave energy and fracturing of ice by wave forcing, and (3) uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies (above the peak). Wave properties during fracturing of ice cover indicated increased groupiness. Wave‐ice interaction presented binary behavior: there was zero transmission in unbroken ice and total transmission in fractured ice. The fractured ice front traveled at some fraction of the wave group speed. Findings do not motivate new dissipation schemes for wave models, though they do indicate the need for two‐way, wave‐ice coupling.
Key Points
Largest waves measured under ice cover in the Arctic
High‐resolution, coupled wave‐ice models are required for accurate predictions
Nonlinearly enhanced waves may lead to initial ice breakup
Abstract
Wave energy propagating into the Antarctic marginal ice zone effects the quality and extent of the sea ice, and wave propagation is therefore an important factor for understanding and ...predicting changes in sea ice cover. Wave‐sea ice interactions are notoriously hard to model and in situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region. Here, we provide new in situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Weddell Sea in the austral winter and spring of 2019. The buoy location ranges from open water to more than 200 km into the sea ice. We estimate the attenuation of swell with wave periods 8–18 s, and find an attenuation coefficient
α
= 4 · 10
−6
to 7 · 10
−5
m
−1
in spring, and approximately five‐fold larger in winter. The attenuation coefficients show a power law frequency dependence, with power coefficient close to literature. The in situ data also shows a change in wave direction, where wave direction tends to be more perpendicular to the ice edge in sea ice compared to open water. A possible explanation for this might be a change in the dispersion relation caused by sea ice. These observations can help shed further light on the influence of sea ice on waves propagating into marginal ice zones, aiding development of coupled wave‐sea ice models.
Plain Language Summary
Changes in the sea ice extent around Antarctica affects the global climate, and it is therefore important to accurately represent sea ice in climate models. One feature that is generally missing in climate models is the interaction between ocean waves and sea ice. Ocean waves change the sea ice, for example, by breaking up ice floes into smaller ones. At the same time, the sea ice reduces the strength of the waves so that the wave height decreases and eventually disappears far into the sea ice. How far into the sea ice waves reach depends both on the size of the waves and on the sea ice, and can be very different depending on for example, ice thickness, size of floes and age. In order to better represent the wave‐sea ice interactions in climate models, simple but accurate models of how fast sea ice reduces the strength of waves is needed. Using wave buoys, we measured the wave activity in the Antarctic sea ice during two expeditions in 2019. We found a notable difference between spring and winter, where the waves were reduced much faster in winter than in spring. This can help to improve predictions of sea ice cover.
Key Points
SWIFT buoy data show that frequency dependence of wave attenuation in Antarctic sea ice follows a power law
Both wave attenuation and the frequency dependence of attenuation were stronger in austral winter than in spring
Observations suggest a change in wave direction in sea ice compared to open water
One of the important problems regarding the tunnel design in seismically active areas is the assessment of the mutual effect of two closely running tunnels. With the propagation of seismic waves, the ...stresses in certain sections of a tunnel, owing to the presence of an adjacent tunnel, can exceed those occurring when considering the single‐tunnel case. In the focus of this study is the hitherto unexplored elastic wave diffraction problem, which considers the influence of the presence of a new‐bored neighbouring cavity on the seismic response of an existing tunnel, under incident P‐waves/SV‐waves. The wave function expansion method, the corresponding boundary conditions along the tunnel and cavity contours, and the translational addition theorem for bi‐cylindrical wave functions are jointly employed to develop an exact mathematical solution of the given problem in the form of infinite FourierBessel series, under the plane‐strain conditions. The dynamic effects of structures are presented in the form of a newly introduced dynamic stress alteration factor as a measure of the variation of dynamic hoop stress amplitudes in the lining and the surrounding medium of an existing tunnel affected by the presence of a closely running newly‐constructed tunnel opening. The results of this study are believed to be useful for interpretation of design rules, particularly considering that seismic standards for tunnels are still in the preliminary stage, where the aspect of the minimum seismically safe distance of a newly‐constructed tunnel opening in the vicinity of an existing tunnel should be of particular concern.
In this paper, the method of combining indirect boundary element method (IBEM) with the region-matching technique is used to solve the seismic responses of a three-dimensional (3D) hill in a layered ...half-space subjected to spherical P, SV, and SH waves. The direct stiffness method and Hankel transform method are used to solve the free field of spherical wave source field, and the scattering field is constructed by Green's function in half-space. The correctness and accuracy of this method are verified by comparing with the results of several literatures. This method can be used to deal with arbitrary-shaped hill topography, and has the advantages of wide applicability, high accuracy and fast convergence. Taking Gaussian hill topography as an example, the scattering phenomenon of hill under the incidence of spherical P, SV and SH waves is studied, and the influences of hill topography, source location and frequency on site seismic responses are explored. The results show that: Existence of the hill topography has evident focusing effect, which significantly enlarges the seismic response on the hill surface, and the hill has evident isolation effect in the process of energy propagation; With higher frequency of the incident wave, the fluctuation amplitude of displacement on the hill surface increases; The fluctuation amplitude of horizontal displacement on the hill surface is SV wave > SH wave > P wave, and the vertical displacement is P wave > SV wave.
•The scattering of spherical P, SV, and SH waves by 3D hill in a layered half-space is studied.•Combining the direct stiffness method and Hankel transform method, the free field of spherical wave source are derived.•Assuming that the incident wave is spherical wave, the near-source topographic effect caused by hills is revealed.•The method can deal with 3D arbitrary-shaped hill topography, and has the merits of high accuracy and easy convergence.
Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. ...The efficiency of wave‐particle resonant interactions is defined by whistler wave properties which have been described by the approximation of plane linear waves propagating through the cold plasma of the inner magnetosphere. However, recent observations of extremely high‐amplitude whistlers suggest the importance of nonlinear wave‐particle interactions for the dynamics of the outer radiation belt. Oblique chorus waves observed in the inner magnetosphere often exhibit drastically nonsinusoidal (with significant power in the higher harmonics) waveforms of the parallel electric field, presumably due to the feedback from hot resonant electrons. We have considered the nature and properties of such nonlinear whistler waves observed by the Van Allen Probes and Time History of Events and Macroscale Interactions define during Substorms in the inner magnetosphere, and we show that the significant enhancement of the wave electrostatic component can result from whistler wave coupling with the beam‐driven electrostatic mode through the resonant interaction with hot electron beams. Being modulated by a whistler wave, the electron beam generates a driven electrostatic mode significantly enhancing the parallel electric field of the initial whistler wave. We confirm this mechanism using a self‐consistent particle‐in‐cell simulation. The nonlinear electrostatic component manifests properties of the beam‐driven electron acoustic mode and can be responsible for effective electron acceleration in the inhomogeneous magnetic field.
Plain Language Summary
We consider the effects of induced scattering of the electromagnetic whistler wave to the electrostatic electron acoustic wave (observed as field‐aligned electric field bursts). The main discussed effect is based on the coupling of the slightly oblique whistler wave and a beam‐driven electron acoustic wave observed as “nonlinear whistler waves”. The wave interaction as the result produces the whistler wave and the rapidly steepening acoustic electrostatic wave with the same phase (and the same k and frequency). Then, because the two different modes are the result of the interaction, the following dynamics of the waves in the inhomogeneous magnetic field is different: the whistler wave phase velocity depends on the background magnetic field magnitude but the acoustic mode propagate with the constant phase velocity. This dynamics leads to the waves phase differences and explains the fact that the observed in the experiment whistler and electrostatic bursts usually have actually random phase shift. To confirm this, we studied the dynamics of these waves in the inhomogeneous magnetic field system making use of the particle‐in‐cell simulation, reproduced all steps of the modes conversion, and confirmed that the dynamics in the inhomogeneous plasma system leads to the observed effects.
Key Points
Nonlinear electrostatic steepening of whistler waves ‐ the induced scattering to electron acoustic waves
Resonant electron beam is highly modulated by a weakly oblique whistler wave
Modulated electron beam initiates the electron acoustic wave turned into the electrostatic nonlinear mode phase related to the whistler
Ross ice shelf vibrations Bromirski, P. D.; Diez, A.; Gerstoft, P. ...
Geophysical research letters,
28 September 2015, Letnik:
42, Številka:
18
Journal Article
Recenzirano
Odprti dostop
Broadband seismic stations were deployed across the Ross Ice Shelf (RIS) in November 2014 to study ocean gravity wave‐induced vibrations. Initial data from three stations 100 km from the RIS front ...and within 10 km of each other show both dispersed infragravity (IG) wave and ocean swell‐generated signals resulting from waves that originate in the North Pacific. Spectral levels from 0.001 to 10 Hz have the highest accelerations in the IG band (0.0025–0.03 Hz). Polarization analyses indicate complex frequency‐dependent particle motions, with energy in several frequency bands having distinctly different propagation characteristics. The dominant IG band signals exhibit predominantly horizontal propagation from the north. Particle motion analyses indicate retrograde elliptical particle motions in the IG band, consistent with these signals propagating as Rayleigh‐Lamb (flexural) waves in the ice shelf/water cavity system that are excited by ocean wave interactions nearer the shelf front.
Key Points
Dispersed swell and infragravity wave‐generated signals are observed 100 km from the shelf front
Polarization analysis indicates infragravity band signal propagation characteristics from the front
IG band signals propagate as Rayleigh‐Lamb (flexural) waves in the ice shelf/water cavity system
We use two‐plane‐wave tomography with a dense network of seismic stations across Sabah, northern Borneo, to image the shear wave velocity structure of the crust and upper mantle. Our model is used to ...estimate crustal thickness and the depth of the lithosphere‐asthenosphere boundary (LAB) beneath the region. Calculated crustal thickness ranges between 25 and 55 km and suggests extension in a NW‐SE direction, presumably due to back‐arc processes associated with subduction of the Celebes Sea. We estimate the β‐factor to be 1.3–2, well below the initiation of seafloor spreading. The LAB is, on average, at a depth of 100 km, which is inconsistent with models that ascribe Neogene uplift to wholescale removal of the mantle lithosphere. Instead, beneath a region of Plio‐Pleistocene volcanism in the southeast, we image a region 50–100 km across where the lithosphere has thinned to <50 km, supporting recent suggestions of lower lithospheric removal through a Rayleigh‐Taylor instability.
Plain Language Summary
Understanding the tectonic processes, which have occurred after subduction has ended, is difficult because: (a) few well‐preserved, recent examples exist on the Earth, and (b) relatively few geophysical images have been made. This study calculates the shear wave velocity (Vsv) of the Earth beneath Sabah, in northern Borneo, using teleseismically detected earthquakes. We use these images of the Vsv to infer that extension dominates the geological history. In addition, we image a region where the lithosphere has dropped off. This correlates with a region of recent volcanism; presumably because of the upwelling hot rock induces melting of the mantle.
Key Points
Shear wave model of Sabah, northern Borneo generated using the two‐plane‐wave method
Crustal thickness and depth to the lithosphere‐asthenosphere boundary indicates back‐arc spreading behind the Celebes Sea slab
In the south‐east corner, the lithosphere has been removed below a region of recent volcanism, possibly due a Raleigh‐Taylor instability
The Xiaojiang fault zone system (XJFS) is located in the southeastern Tibet with high seismicity. In this study, we invert Rayleigh and Love wave dispersion curves obtained from three dense seismic ...arrays jointly for high-resolution 3-D crustal average shear wave velocity and radial anisotropy models simultaneously in XJFS. Our model reveals that the upper crust and mid-lower crust generally exhibit negative and positive radial anisotropy, respectively, implying that the deformation pattern is depth-dependent. To the east of the Lvzhijiang Fault, most of the low velocity zones in the mid-crust correspond to the positive radial anisotropy (Vsh > Vsv); the channelized weak zone seems to be continuous across the Red River Fault at depth of 20 km, probably within a thin layer. West of the Lvzhijiang Fault, where it is inferred to be the inner zone of the Permian Emeishan Large Igneous Province, the high velocity zone and positive radial anisotropy in the mid-lower crust can be attributed to the underplating and intruded magmatic rocks. In the upper crust, the high and low velocity zones are mostly belt-shape and follow the north-south direction parallel to the regional major faults; the lateral variation of the radial anisotropy spatially corresponds to the activity of different segments of the Xiaojiang fault zone. Our models depict detailed geometry of the channelized weak zone in the mid-lower crust and provide new insight into the role of major faults in regional tectonics.
•High-precision crustal Vs and radial anisotropy models in XJFS (SE Tibet) are derived.•Our models depict detailed geometry of the channelized weak zone in mid-lower crust.•Radial anisotropy is spatially associated with activity of different segments of XJF.
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